The present invention relates to a pneumatic radial tire.
In order to conserve the global environment, attempts are being made to make automobiles more fuel-efficient. Therefore, with respect to tires for automobiles, tires with low rolling resistance are desired and particularly, lower rolling resistance is desired for heavy load tires used for heavy load vehicles such as trucks and buses, which have large displacement volume and fuel consumption.
Rolling resistance of a tire is largely affected by energy loss, which accompanies repeated deformation while running. Consequently, in order to reduce rolling resistance, for example, a tire structure is suggested, in which the rubber for the tread, which has the highest contribution rate (about 34%) for reducing rolling resistance, is composed of two layers, the inner layer being made of compound rubber having small energy loss and the outer layer being made of compound rubber having excellent gripping performance.
However, while the tread contributes largely to reducing rolling resistance, the tread also contributes largely to abrasion resistance, performance on snow and performance on wet surfaces. Particularly, reduction of rolling resistance is often in antinomy with such running performance. Therefore, there is the problem that by reducing rolling resistance, running performance tends to be lost.
Attempts are being made to improve toe-chip resistance and bead durability by improving the tensile properties of chafer rubber positioned at the bead of heavy load tires (see JP-A-2001-226526). In addition, attempts are made to improve bead durability and reduce rolling resistance by improving the dynamic viscoelasticity of the sidewall packing rubber (see JP-A-2002-178724). However, these methods do not consider low heat generation in chafer rubber and have the problem that rolling resistance cannot be reduced further.